This application is based on application No. 11-297773 filed in Japan, the content of which is hereby incorporated by reference.
(1) Field of the Invention
The present invention relates to a discharge lamp, an electrode used for a discharge lamp, and a method for producing an electrode.
(2) Description of the Prior Art
A conventional discharge lamp electrode is disclosed in the xe2x80x9cpublication of examined utility model applicationxe2x80x9d No. 38-26740 in Japan, for instance. FIG. 1A shows a conventional discharge lamp electrode. As shown in the figure, the discharge lamp electrode 900 is formed by winding a single wire 902 around an electrode rod 901 so that the wire 902 forms a double-layer coil construction composed of a first-layer coil 911 and a second-layer coil 912. More specifically, the wire 902 is wound from a predetermined portion of the electrode rod 901 toward a discharge-side end 910 of the electrode rod 901, and then from the discharge-side end 910 back toward the opposite side so that the first-layer coil 911 and the second-layer coil 922 each have an opposite xe2x80x9cturning directionxe2x80x9d. Here, the xe2x80x9cturning directionxe2x80x9d refers to either a clockwise direction or a counterclockwise direction, in which the wire 902 turns when viewed from an end of the electrode rod 910 from which the wire 902 is wound away. In FIG. 1A shown as an example, the wire 902 forming the first-layer coil 911 is turned clockwise, while the wire 902 forming the second-layer coil 912 is turned counterclockwise.
In this way, the conventional electrode 900 is produced by winding the wire 902 around the electrode rod 901 to form a double-layer coil construction, and cutting the wire 902 to a predetermined length.
However, the conventional electrode 900 has the following problems.
First, as can be understood from FIG. 1B which is a front view of the discharge-side end 910 of the electrode 900, the electrode 900 contains a portion, where the above turning direction changes, that has a single-layer coil construction.
Second, for the conventional electrode 900, interstices exist between the first-layer coil 911 and the second-layer coil 912, so that a heat capacity of an end portion of the electrode 900 becomes insufficient. This raises a temperature of the end portion, and therefore the end portion becomes liable to melt and vaporize, and eventually electrode substances are scattered inside a light-emitting tube. This causes wall blackening inside the light-emitting tube and degrades luminance of light emitted from the light-emitting tube at an earlier stage of use of the lamp.
Thirdly, when the discharge-side end 910 melts and gets deformed, the second-layer coil 912 gradually moves toward the discharge-side end 910, and is melt and scattered in accordance with an increase in a temperature of the discharge-side end 910. This further intensifies blackening inside the light-emitting tube.
Development of a downsized projector with a liquid crystal panel has been continued. This therefore requires a discharge lamp, which is used as a light source of such projector, to have a shorter arc. A shorter arc results in increasing the temperature of the end portion of the electrode 900, but a longer life is still required for such discharge lamp. Accordingly, development of a discharge lamp electrode that can satisfy these needs is now urgently demanded.
The present invention aims to provide a discharge lamp electrode whose end portion deformations are suppressed so that the electrode has a longer life, a discharge lamp for which the electrode is used, and a method for producing an electrode for a discharge lamp with increased productivity.
The above object can be achieved by a discharge lamp electrode used for a discharge lamp. The electrode includes: an electrode rod made of refractory metal; and a winding element made of refractory metal wires that are wound around the electrode rod in a same turning direction and that forms n layers of coils, n being larger than one, wherein a wire forming an (m+1)th layer is wound along a spiral valley between adjacent turns in a coil of an mth layer, m satisfying an inequality 0 less than m less than n, an ordinal number given to each layer representing an order in which a coil of the layer has been formed.
For this construction, a wire forming the (m+1)th layer of a coil is wound along a spiral valley between turns in a coil of the mth layer. This construction prevents the outer layer of the coil from moving toward the discharge side when an end of the electrode melts or vaporizes to be deformed due to an increase in a temperature of the electrode end while the light is lit. As a result, further deformations at the electrode end can be suppressed, and therefore a life of a discharge lamp is extended.
The method for producing a discharge lamp electrode according to the present invention is characterized by including: a winding step for winding at least one refractory metal wire around a core member and forming n layers of coils one by one, n being larger than one; a cutting step for cutting the formed n layers of coils and the core member; a removing step for removing the core member after the cutting step; a rod inserting step for inserting an electrode rod into a space from which the core member has been removed, the electrode rod being made of refractory metal; and a fixing step for fixing the formed n layers of coils to the inserted electrode rod.
With this method, metal wires do not have to be wound around each electrode rod to form layers of coils for each electrode, so that productivity of electrodes can be improved.